feat(pre_seed): support .tar.gz/.tgz archives

[chaodu-agent]

Summary

Adds tarball extraction to the pre_seed phase, so existing .tar.gz home backups can be consumed directly without migration to zip.

Format Detection

Based on S3 URI extension:

• .zip → zip extraction (existing)
• .tar.gz / .tgz → gzipped tarball extraction (new)

Example

[hooks.pre_seed]
sources = [
  "s3://openab-state-pahud/chaodu-home.tar.gz",    # existing tarball
  "s3://openab-state-pahud/shared/openab.zip",     # zip also works
]

Implementation

• Uses flate2 (gzip decompression) + tar (archive extraction)
• Same safety limits: max file count, max extracted bytes, cooperative deadline
• Preserves Unix permissions
• Feature-gated under pre-seed

Tests

All 10 existing tests pass. Tarball extraction shares the same budget/deadline infrastructure.

[chaodu-agent]

Note

LGTM ✅ — All findings from group review addressed in 8494cd8.

What This PR Does

Adds .tar.gz/.tgz extraction support to the pre_seed phase, allowing existing tarball home backups to be consumed directly without migration to zip format.

How It Works

Format auto-detected via gzip magic bytes (0x1f, 0x8b) — no URI extension dependency. Uses flate2 for decompression + tar crate (≥ 0.4.45, CVE-2026-33056 patched) for extraction. Same budget/deadline infrastructure as zip path. Extracts atomically via temp directory.

Review Summary

Group review identified 2 critical + 5 important findings. All were fixed in commit 8494cd8. Re-review confirmed all fixes.

Findings

#	Severity	Finding	Resolution
1	🔴	Cargo.lock missing tar crate — build not reproducible	✅ Fixed — lockfile updated with tar 0.4.46 + filetime
2	🔴	CVE-2026-33056: tar = "0.4" allows vulnerable versions	✅ Fixed — pinned "0.4.45", default-features = false
3	🟡	set_preserve_permissions(true) preserves suid/sgid bits	✅ Fixed — disabled, manual chmod with & 0o0777 mask
4	🟡	URI extension detection fragile (case-sensitive, query params)	✅ Fixed — magic bytes [0x1f, 0x8b] detection, uri param removed
5	🟡	No tarball-specific unit tests	✅ Fixed — 3 tests added (basic, magic bytes, deadline)
6	🟡	Deadline check only every 100 files	✅ Fixed — reduced to every 10 files
7	🟡	entry.size() relies on header-declared value	ℹ️ Accepted — low risk, tar crate limits reads internally
8	🟢	Atomic extraction via temp directory	Excellent design ✅
9	🟢	unpack_in correctly prevents path traversal	Confirmed ✅

Follow-up Suggestions (non-blocking)

• Add extract_tarball_budgeted(..., max_file_count, max_extracted_bytes) helper + small tar limit tests to mirror zip test coverage
• Add --features pre-seed to CI workflow for compile/test coverage
• Consider post-extraction size verification via std::fs::metadata for defense-in-depth against gzip bombs

Baseline Check

• PR opened: 2026-06-25
• Main already has: zip-based pre_seed with full safety infrastructure (budget, deadline, path traversal protection)
• Net-new value: tarball format support for existing .tar.gz backups without format migration

What's Good (🟢)

• Atomic extraction pattern prevents corrupted state on failure
• unpack_in correctly handles path traversal protection
• Clean feature-gating under pre-seed
• Reuses existing budget/deadline infrastructure
• Magic bytes detection is robust against filename variations